/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.hcatalog.hbase.snapshot.lock;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Stat;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * A base class for protocol implementations which provides a number of higher
 * level helper methods for working with ZooKeeper along with retrying synchronous
 *  operations if the connection to ZooKeeper closes such as
 *  {@link #retryOperation(ZooKeeperOperation)}
 *  This class has been used as-is from the zookeeper 3.4.0 recipes with
 *  changes in the retry delay, retry count values and package name.
 */
class ProtocolSupport {
  private static final Logger LOG = LoggerFactory.getLogger(ProtocolSupport.class);

  protected final ZooKeeper zookeeper;
  private AtomicBoolean closed = new AtomicBoolean(false);
  private long retryDelay = 500L;
  private int retryCount = 3;
  private List<ACL> acl = ZooDefs.Ids.OPEN_ACL_UNSAFE;

  public ProtocolSupport(ZooKeeper zookeeper) {
    this.zookeeper = zookeeper;
  }

  /**
   * Closes this strategy and releases any ZooKeeper resources; but keeps the
   *  ZooKeeper instance open
   */
  public void close() {
    if (closed.compareAndSet(false, true)) {
      doClose();
    }
  }

  /**
   * return zookeeper client instance
   * @return zookeeper client instance
   */
  public ZooKeeper getZookeeper() {
    return zookeeper;
  }

  /**
   * return the acl its using
   * @return the acl.
   */
  public List<ACL> getAcl() {
    return acl;
  }

  /**
   * set the acl
   * @param acl the acl to set to
   */
  public void setAcl(List<ACL> acl) {
    this.acl = acl;
  }

  /**
   * get the retry delay in milliseconds
   * @return the retry delay
   */
  public long getRetryDelay() {
    return retryDelay;
  }

  /**
   * Sets the time waited between retry delays
   * @param retryDelay the retry delay
   */
  public void setRetryDelay(long retryDelay) {
    this.retryDelay = retryDelay;
  }

  /**
   * Allow derived classes to perform
   * some custom closing operations to release resources
   */
  protected void doClose() {
  }


  /**
   * Perform the given operation, retrying if the connection fails
   * @return object. it needs to be cast to the callee's expected
   * return type.
   */
  protected Object retryOperation(ZooKeeperOperation operation)
    throws KeeperException, InterruptedException {
    KeeperException exception = null;
    for (int i = 0; i < retryCount; i++) {
      try {
        return operation.execute();
      } catch (KeeperException.SessionExpiredException e) {
        LOG.warn("Session expired for: " + zookeeper + " so reconnecting due to: " + e, e);
        throw e;
      } catch (KeeperException.ConnectionLossException e) {
        if (exception == null) {
          exception = e;
        }
        LOG.debug("Attempt " + i + " failed with connection loss so " +
                "attempting to reconnect: " + e, e);
        retryDelay(i);
      }
    }
    throw exception;
  }

  /**
   * Ensures that the given path exists with no data, the current
   * ACL and no flags
   * @param path
   */
  protected void ensurePathExists(String path) {
    ensureExists(path, null, acl, CreateMode.PERSISTENT);
  }

  /**
   * Ensures that the given path exists with the given data, ACL and flags
   * @param path
   * @param acl
   * @param flags
   */
  protected void ensureExists(final String path, final byte[] data,
      final List<ACL> acl, final CreateMode flags) {
    try {
      retryOperation(new ZooKeeperOperation() {
        public boolean execute() throws KeeperException, InterruptedException {
          Stat stat = zookeeper.exists(path, false);
          if (stat != null) {
            return true;
          }
          zookeeper.create(path, data, acl, flags);
          return true;
        }
      });
    } catch (KeeperException e) {
      LOG.warn("Caught: " + e, e);
    } catch (InterruptedException e) {
      LOG.warn("Caught: " + e, e);
    }
  }

  /**
   * Returns true if this protocol has been closed
   * @return true if this protocol is closed
   */
  protected boolean isClosed() {
    return closed.get();
  }

  /**
   * Performs a retry delay if this is not the first attempt
   * @param attemptCount the number of the attempts performed so far
   */
  protected void retryDelay(int attemptCount) {
    if (attemptCount > 0) {
      try {
        Thread.sleep(attemptCount * retryDelay);
      } catch (InterruptedException e) {
        LOG.debug("Failed to sleep: " + e, e);
      }
    }
  }
}
